Ammoxidation of propane to acrylonitrile

In current process technology for the manufacture of acrylonitrile, propene feedstock cost represents about 67% of the cost of production. The price differential between 

Catalyst Conditions Conversion of Selectivity for Selectivity for Reference 

Asahi [29] has modified the composition of the Mitsubishi catalyst, by incorporation of Sb in place of Te in the Ml phase this catalyst is more stable and 

A third catalytic system was proposed more recently and based on vanadium aluminum oxynitrides (VALON) [30]. The maximum acrylonitrile yield reported was about 30%, but with acrylonitrile productivity four times higher than for V/ Sb/W/Al/O catalysts and one order of magnitude than for Mo/V/Nb/Te/O. Other companies have studied and developed proprietary formulations but, in general, catalytic systems belong either to the antimonates family (Rhodia, BASF, Nitto, Monsanto) [31-33] orto the molybdates family. 

Therefore, the catalyst possesses different types of active sites one site that can activate the paraffin and oxide hydrogenate it to the olefin, and one that (amm) oxidizes the adsorbed olefin intermediate. 

For the catalyst based on Mo10V0.33Nb0.nTe0.22Ox, a precise phase composition is claimed, as defined by the ratio of the X-ray diffraction peak intensity at 20 27.3° and 28.2° (CuKa), which minimizes the combustion of ammonia to N2 [29d,j]. 

For instance, when the degree of ammonia decomposition is only 29.4%, the yield to acrylonitrile is 58.9% at 93.1% propane conversion, with a feed composition propane/ammonia/oxygen/inert equal to 1.0 1.2 3.0 14.8, at 420 °C and W/F 0.5 g s cc . When the same active phase is diluted in silica by means of the spraydrying procedure, the best yield to acrylonitrile achieved is 52.7% at 430 °C [29e], but the addition of a dopant (Yb, Er, Dy, Nd, etc.) increases the yield up to 55-56%. Dopants also allow the feed of a lower ammonia/propane ratio, for example, 0.8 instead of the stoichiometric 1.0, while reaching in high yield to acrylonitrile with respect to ammonia, and minimizing ammonia combustion [29h]. 

---

Numerous patents have been issued disclosing catalysts and process schemes for manufacture of acrylonitrile from propane. These include the direct heterogeneously cataly2ed ammoxidation of propane to acrylonitrile using mixed metal oxide catalysts (61—64). 

The increasing volume of chemical production, insufficient capacity and high price of olefins stimulate the rising trend in the innovation of current processes. High attention has been devoted to the direct ammoxidation of propane to acrylonitrile. A number of mixed oxide catalysts were investigated in propane ammoxidation [1]. However, up to now no catalytic system achieved reaction parameters suitable for commercial application. Nowadays the attention in the field of activation and conversion of paraffins is turned to catalytic systems where atomically dispersed metal ions are responsible for the activity of the catalysts. Ones of appropriate candidates are Fe-zeolites. Very recently, an activity of Fe-silicalite in the ammoxidation of propane was reported [2, 3]. This catalytic system exhibited relatively low yield (maximally 10% for propane to acrylonitrile). Despite the low performance, Fe-silicalites are one of the few zeolitic systems, which reveal some catalytic activity in propane ammoxidation, and therefore, we believe that it has a potential to be improved. Up to this day, investigation of Fe-silicalite and Fe-MFI catalysts in the propane ammoxidation were only reported in the literature. In this study, we compare the catalytic activity of Fe-silicalite and Fe-MTW zeolites in direct ammoxidation of propane to acrylonitrile. 

The synthesis of intermediates and monomers from alkanes by means of oxidative processes, in part replacing alkenes and aromatics as the traditional building blocks for the chemical industry [2]. Besides the well-known oxidation of n-butane to maleic anhydride, examples of processes implemented at the industrial level are (i) the direct oxidation of ethane to acetic acid, developed by Sabic (ii) the ammoxidation of propane to acrylonitrile, developed by INEOS (former BP) and by Mitsubishi, and recently announced by Asahi to soon become commercial (iii) the partial oxidation of methane to syngas (a demonstration unit is being built by ENI). Many other reactions are currently being investigated, for example, (i) the... 

Acrylonitrile is commercially produced from propylene by a molybdate-based catalyst that has been optimized to produce a yield of around 80% acrylonitrile. Utilizing a less-expensive feedstock, the selective ammoxidation of propane to acrylonitrile has significant potential in reducing acrylonitrile production cost. The work-flow for this chemistry consisted of a primary scale evaporative synthesis station and 256-channel parallel screening reactor using a proprietary optical-based detection method. For the initial work shown here, secondary screening was done on a six-channel fixed-bed reactor. 

Supporting the vanadium phosphate material on silica 286,293,296-298) or titania 285) has proved beneficial, giving catalysts that provide increased MA yields (20M0%) 297). This observation is in contrast to the results of a number of investigations that indicated the reverse 299,300). Investigations of the ammoxidation of propane to acrylonitrile showed that competitive adsorption of NH3 and O2 could direct the selectivity 88). 

The aim of this review is to describe the reactivity of three catalytic systems whieh have been widely studied in recent years for the oxidative tran.sformation of light paraffins i) vanadyl pyrophosphate, which is the industrial catalyst for the oxidation of /i-butane, but has also been elaimed to be selective in the oxidation of n-pentane to maleie and phthalic anhydrides (18-22), ii) heteropolyeompounds, whieh are currently being studied for the oxidation of isobutane and propane to the corresponding unsaturated acids (methacrylic acid and acrylic acid) (5,23-29), and whose composition can be tuned to change the acidic and oxidizing properties and iii) rutile-based mixed oxides, which can act as the matrix to host various metal components, and whieh have been claimed as optimal eatalysts for the ammoxidation of propane to acrylonitrile (15,30-33). 

Mo-V-Nb-Te mixed oxides are amongst the most active and selective catalysts in the ammoxidation of propane to acrylonitrile (ACN) [1-3]. The activity of these catalysts is assumed to be associated with two phases (called Ml and M2) namely orthorhombic Mo7.gVi.2NbTeo.94028.9 (Ml) and pseudo-hexagonal M04.67V1.33Te1.82O19.g2 (M2). The exact role of the two phases is not yet fully understood but it has been reported that their concomitant presence is necessary to generate effective catalysts [4-5]. It is supposed that the Ml phase is responsible for the paraffin activation and that the M2 phase is rather ineffective for this reaction and thus plays a promotor role for Ml. 

In addition to these general comments, it may be adequate to mention here an example of potential practical interest, but possibly corresponding of a very particular case, actually a narrow alley. Oxynitrides were first studied as catalysts by Grange. One member of the family studied in his laboratory is extremely active and selective in the ammoxidation of propane to acrylonitrile (37-39). Even with the nonmodified, nondoped catalysts, a selectivity of 60% is easily achieved at 500°C with a productivity (e.g., per kilogram per hour) over 10 times higher than with the catalysts mentioned in literature. The catalyst is obtained by the action of ammonia on amorphous AlVi. Oy. This mixed oxide remains amorphous below 400°C, allowing... 

The inorganic chemistry of a multi-component heterogeneous catalyst is often very complex, as it is quite difficult to obtain structural information at the molecular level to help establish the fundamental processes. As an example, we discuss the chemistry of the complex mixed metal oxide catalyst Mo7,5Vi,5NbTe029 shown in Fig. 2.25, which is known to catalyze the ammoxidation of propane to acrylonitrile. The active centers in this system are multifunctional metal oxide assemblies that are spatially isolated from one another owing to their unique crystal structures. 

One important characteristic of V-Sb-0 based catalysts, initially developed for the partial ammoxidation of propane to acrylonitrile in the 1980s by BP, is the presence of cation-deficient rutile-type VSb04 (Fig. 24.2b) and a-Sb204 structures. Antimony is mainly present in a pentavalent state favoring a large amount of partially reduced vanadium species, with the formation of V Sb04 and the possible presence of in substitutional or interstitial solid solution coordinations. The... 

Guerrero-Perez, M., Al-Saeedi, J., Gnliants, V., et al. (2004). Catalytic Properties of Mixed Mo-V-Sb-Nb-O Oxides Catalysts for the Ammoxidation of Propane to Acrylonitrile, Appl. Catal. A Gen., 260, pp. 93-99. 

The results from selected patents for the ammoxidation of propane to acrylonitrile are shown in Table 9.2. Significant advances have been made over the past 10 years. High conversions and selectivi-ties approaching 64% have been obtained. BP has announced that a pilot plant is operational to collect basic data for commercial design. The stake is high for this development because of the lower cost of propane compared to propylene and the reduction in CO2 emissions. 

TABLE 9.2 Selected Results for Ammoxidation of Propane to Acrylonitrile... 

---